The main difference from choosing a different subset, e.g. “Google C++” (i.e. writing C++ according to the Google style guide), is that the compiler enforces that you stick to the subset.
Oh, and smart pointers too.
And hash maps.
Vectors too while we're at it.
I think that's it.
The latter two (hash maps and vectors), though, are just compound data types that can be built on top of standard C. All it would need is to agree on a new common library, more modern than the one designed in the 70s.
Yes, SDS exists, however vocabulary types are quite relevant for adoption at scale.
I think you want the string slice reference type, what C++ called std::string_view and Rust calls &str. This type is just two facts about some text, where it is in memory and how long it is (or equivalently where it ends, storing the length is often in practice slightly faster in real machines so if you're making a new one do that)
In C++ this is maybe non-obvious because it took until 2020 for C++ to get this type - WG21 are crazy, but this is the type you actually want as a fundamental, not an allocating type like std::string.
Alternatively, if you're not yet ready to accept that all text should use UTF-8 encoding, -- and maybe C isn't ready for that yet - you don't want this type you just want byte slice references, Rust's &[u8] or C++ std::span<char>
Hash maps are mostly only important because everyone ought to standardize on a way of hashing keys.
But I suppose they can both be “bring your own”… to me it’s more that these types are so fundamental and so “table stakes” that having one base implementation of them guaranteed by the language’s standard lib is important.
And it wasn't hard to achieve. The idea was to use length delimited strings rather than 0 terminated. This meant that slices of strings being strings is a superpower. No more did one have to constantly allocate memory for a slice, and then keep track of that memory.
Length-delimited also super speeded string manipulation. One no longer had to scan a string to find its length. This is a big deal for memory caching.
Static strings are length delimited too, but also have a 0 at the end, which makes it easy to pass string literals to C functions like printf. And, of course, you can append a 0 to a string anytime.
One of the fun things about Empire is one isn't out to save humanity, but to conquer! Hahahaha.
BTW, one of my friends is using ClodCode to generate an Empire clone by feeding it the manual. Lots of fun!
And const references.
And lambdas.
So that wouldn't really fit C very well and I'd suggest that Rust's String, which is essentially just Vec<u8> plus a promise that this is a UTF-8 encoded string, is closer.
The differences are the usual that occur with guest languages, in this case the origin being UNIX and C at Bell Labs, eventually each platform goes its own merry way and compatibility slowly falls apart with newer versions.
In regards to C89 the main differences are struct and unions naming rules, () means void instead of anything goes, ?: precedent rules, implicit casts scenarios are reduced like from void pointers.